This invention relates to the control of energy transfer between a storage inductor and a load inductor through the use of a polyphase bridge.
A number of applications require the transfer of relatively large amounts of electrical energy into a coil. These applications include coils for the principal magnetic fields in synchrotron and other circulating particle accelerators and they include coils such as the ohmic heating coil and various confinement coils in proposed Tokamak power reactors. For applications such as these that require substantial amounts of power to be delivered to the coil, it is desirable to transfer the energy between a storage unit and the coil with little energy loss in the process rather than transfer the energy into and out of the utility grid when the associated magnetic field of the coil is reduced or increased. One way that has been proposed to do this is to use inductor-converter units that include a storage inductor connected to a polyphase bridge rectifier. The bridge rectifier is connected to an array of commutating capacitors and then to a second polyphase bridge rectifier which is connected to the load inductor or coil. Examples of the type of circuit described are given in a paper entitled "Superconductive Inductor-Convertor Units for Pulsed Power Loads" by Peterson, Mohan, Young, and Boom, published in the proceedings of the Conference on Energy Storage, Compression and Switching, November 5-7, 1974, Plenum Press, N.Y. 1976. Similar circuits are shown in Peterson and Mohan, U.S. Pat. No. 4,053,820, entitled "Active Filter". The paper and the patent deal first with the situation in which an ac power system is connected through a bridge to a storage inductor, especially a superconducting storage inductor which can in principle store large amounts of energy. Control of such a system is relatively straightforward because the ac system dominates the conduction through elements of a thyristor bridge by the fact that voltages are applied as supplied by the system. The references go on to indicate a circuit of the type that is controlled by the method and means of the present invention. However, where there is no dominant source such as a power system to control applied voltages, then the switching of thyristors in bridges to transfer energy from one inductor to another presents two problems. One is that of maintaining balance in the thyristor elements by controlling switching during relative and arbitrary changes. A second is to use the commutating capacitors optimally by charging them fully without overcharging.
It is an object of the present invention to provide an improved method of controlling the operations of an inductor-convertor unit. Other objects will become apparent in the course of a detailed description of the invention.